Semiconductor devices, i.e., magnetic random access memory (MRAM) devices use magnetic memory cells to store information. A cell is typically a submicron piece of magnetic material. The magnetic memory cell may be an ellipse, having the dimensions, e.g., of 300 nanometers (nm) by 600 nm in area and five nm thick.
Information is stored in the device as the direction of the magnetization of a free layer in the magnetic memory cell, pointing either right or left, to store either a “1” or a “0.” When the cell is sitting in a zero applied magnetic field, the magnetization of the cell is stable, pointing either right or left. The application of a magnetic field can switch the magnetization of the free layer from right to left, and vice versa, to write information to the cell.
One of the objectives of MRAM is to have a low operating power and a small area. These objectives require a low switching field for the magnetic memory cell, because a low switching field uses a low switching current, which uses less power, and because smaller currents require smaller switches, which occupy less space. Therefore, another objective of MRAM is to reduce the field required to switch the cells.
In MRAM devices there are an array of magnetic memory cells. One cell is written by sending current down a bit line and a word line. In theory, the cell at the intersection of these two lines experiences both an easy and a hard axis field, and thus switches. The easy axis is the axis along the direction the magnetization typically lies and the hard axis is perpendicular to this easy axis. Cells on the column line only feel the easy axis field (a half select field), and the cells on the row line only feel the hard axis field (half select field). These half selected cells are not meant to be switched. However, during actual operation of an MRAM device, factors, such as variations in the device, cause some of the half selected cells to be arbitrarily switched, placing the reliability and validity of the stored data in question.
Thus, it would be desirable to have a semiconductor device with a low operating power and a small area, and wherein the arbitrary switching of half selected cells is reduced or eliminated.